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Jbtsax's Moving The Mouthpiece - Derin Insert Tests

This is an interesting topic. I hope you don't mind my migrating it here from over there. It seemed to have bogged down. Understanding why your instrument/mouthpiece behaves the way it does can only improve your musicianship and your music. Here's jbtsax's summary:
"A - The alto saxophone is tuned to A=440. A 1/4" wide delrin ring the same dimensions as the end of the neck is inserted into the shank of the mouthpiece. The mouthpiece is set onto the neck 1/4" lower than before.
The saxophone's tuning is exactly the same on the A=440 tuning note, and the pitch relationships up and down the scales are the same as when the mouthpiece was in the original tuned position on the cork.
Conclusion: Adding to the physical length of the saxophone as measured from the tip of the mouthpiece to the first open hole has no effect upon the pitch produced by the instrument or its intonation provided the volume inside the mouthpiece remains constant (unchanged).
B - The saxophone is tuned to A=440 with the delrin insert in the shank of the mouthpiece. The pitch relationships throughout the range are the way the saxophone normally plays (see above). The insert is removed from the shank of the mouthpiece and the mouthpiece is pushed onto the cork an additional 1/4". Again the saxophone plays in tune to A=440 and the pitch relationships (intonation) remains consistent with the way the sax normally plays.
Conclusion: Subtracting from the physical length of the saxophone as measured from the tip of the mouthpiece to the first open hole has no effect upon the pitch produced by the instrument or its intonation provided the volume inside the mouthpiece remains constant (unchanged)."
I duplicated jbtsax's findings on a tenor sax using a similar insert and his conclusions are good, but one needs to go a little deeper in order to see what is happening and why. We are assuming that the truncation is at the small end of the neck.
The conical instrument needs the following in order to function:
1. a body tube
2. a mouthpiece chamber
3. a constriction between 1 and 2.
The total volume of the mouthpiece chamber AND the constriction should equal the missing cone piece of the truncated cone. As the end of the neck is the smallest point of the bore, that is obviously and effectively our constriction, but as the neck is not part of the truncation, our constriction has no length. It is effectively 2 dimensional - for now. The mouthpiece chamber and throat are all considered chamber volume, and regardless of shape, they behave as a cylindrical tube (with perturbations).
When we add to the physical length of the saxophone as in "A" above, by inserting a 1/4" long cylindrical tube, the same diameter as the neck opening, into the throat of the mouthpiece, and then pull the mouthpiece out 1/4" to get our tuning right, we have reduced the volume of the effective mouthpiece chamber (chamber+throat) and given our 2 dimensional constriction 1/4" of length and respective volume. The total volume of chamber + constriction remains the same. One can vary the chamber/constriction volume ratio this way (A) and that (B), and as long as the combined volume AND the resonance frequency of their combined length matches that of the theoretical truncation, the tuning will be OK, both in low and high registers.
What is going on? While the mouthpiece volume + constriction volume=truncation volume, the mouthpiece and the constriction are still 2 separate parts. One is not the other. Changing the length will always affect the pitch. No explanation necessary. Changing volume will always affect pitch as well WHEN IT OCCURS AT A COMPRESSION ANTI-NODE (or displacement-antinode) AND the mouthpiece chamber is a pressure anti-node for every note on the horn. In "A" we inserted the 1/4" constricton into the mouthpiece throat and pulled the mouthpiece out 1/4". The extra length made the general pitch lower, but the constriction displaced some of the mouthpiece volume. Since the mouthpiece chamber is a pressure anti-node, the pitch general pitch of everything was raised. So the intonation did not change. Same thing in reverse for B.
In one of my tests I enlarged my link chamber to where it would not play in tune at all, regardless of where the mouthpiece was placed. While I could push in to get a good A=440, the upper register was sharp of course. Even though the volume of the mouthpiece/2 dimensional constriction was right, the resonant frequency of their combined lengths was too high. By inserting a 1/2" constriction insert into the throat of the mouthpiece and pulling back out appropriately, both the combined mouthpiece/constriction volume and their resonant frequency matched that of the theoretical truncation, and the intonation was as close to perfect as it could be, in every register.
Notes:
1. In actuality, the constriction tube wall volume displacement/constriction tube bore displacement ratio is never exactly 1/1, so putting a 1/2" constriction doesn't equal pulling out 1/2" exactly.
2. The effective mouthpiece volume in playing conditions is significantly larger than the hard-walled, closed reed, geometrical measurement. Add the volume of the reed and it's arc at it's widest point at least.
3. Amplitude (pp - ff) and embouchure variations (vibrato, bends, etc) also change the effective mouthpiece volume. One need look for a mean volume, that takes this into account to base everything on.

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Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

If you experiment with inserts or neck extensions, it is of utmost importance that they fit the shank of the mouthpiece perfectly. If there is even the slightest gap between the two (and a thinner gap is worse than a wider one) there will be loss of energy, excessive turbulence, and possibly strange noises and response behaviour. Best make the insert very slightly undersized and wrap completely with the THINNEST tech-cork. The cork will also suck up sound so thiner is better.

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

And one correction. When you add a constriction insert, you don't pull out the length of the insert. You pull out enough to equal the displacement of the insert's wall volume only. Otherwise the combined mouthpiece+constriction volume will be too large. The same goes in reverse.

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

Hey there- glad to see you're still posting (though I'm still dubious on the flat resos being "what was intended" for ALL sax's by their designers .....!) I forward for you consideration a request by John (JBTSax) that you continue this thread at ; groups.google.com/group/alt.music.saxophone/topics which gets you alt.sax.... JBT managed to get into a spirited debate here with Vodemort and so can no longer enter the discussion here.
I point out that while there are certainly interested people sho could both appreciate and contribute to this thread there it IS an unmoderated forum and there's a low "signal to noise ratio" in many threads.
Interesting topic- as you have time you might address, if so inclined, the contrast between normal mouthpiece pulling and thuning down my lengthening the neck as with a Conn microtuner.
Good to see you in any case. Henry

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

Thanks Henry, FYI, on my own initiative, I resigned my SOTW membership, in protest of the administration's censorship policy. I was not thrown out, though they would like to have it appear that way. Lol.
I responded to jbtsax on the alt.music.saxophone Jungle Forum. Very funny stuff over there.
Lance

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

Thanks- I saw your post. It should prove an interesting discussion though you may well have to ignore four out of five posts and it may, on a frequent basis, try your self control.
I personally was unable to put up with the BS and so have dropped off that forum, though I still stop by to get the sax equivalent of a supermarket checkout tabloid. Actually participating on the board was too much for me- gave me more grief than pleasure.
Interesting idea on the resos. I am completely willing to acknowlege merit in such a concept- nibbling round the edges or not it appears to have a sound basis in acoustic fact. Implementing it.....hoo boy!
Henry

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

MartinMods,
Did you get tired of beating the dead horses on other forums and decided to bring them here? I'd be happy to help with your legitimate repair concerns and questions that are new. But please leave the "I'm smater than you" stuff elsewhere. In this forum that is kindly sponsored by this business, we can actually help folks.

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

Re: Jbtsax's Moving The Mouthpiece - Derin Insert Tests

Although It's boring to me to read all of Martinmods
"I'm Smarter than you" stuff, I am sure it really turns on a certain type of person. For me, I am interested in playing the horn, I could care less how it works, but I am grateful to these egg heads who keep on doing their thing and keep fixing the players horns.........Kelsey